DE102017113451A1 - Method and device for controlling the reduction agent injection into an exhaust gas inlet of an internal combustion engine - Google Patents

Abstract

An exhaust aftertreatment system including a selective catalytic reduction device (SCR), a NOx sensor and a reductant injection system is described. One method of controlling the reductant injection system to inject reductant into the upstream exhaust relative to the SCR includes monitoring engine operation and determining an initial reductant dosing rate responsive to engine operation. A dosing disorder is induced in the reducing agent dosage rate. The exhaust gas feed is monitored via the NOx sensor and a reductant dosing correction term is determined based on the monitoring. A final dosage rate for controlling the reductant injection system is determined based on the initial reductant dosing rate, the dosing error, and the reductant dosing correction term

Description

TECHNICAL AREA

This disclosure relates to internal combustion engines in fluidized association with exhaust aftertreatment systems and to methods of controlling same.

BACKGROUND

Internal combustion engines are fluidly connected to exhaust aftertreatment systems which clean the exhaust gases generated as combustion waste products. The exhaust aftertreatment systems may include oxidation catalysts, reduction catalysts, selective catalytic reduction catalysts, and particulate filters. Combustion waste products may include unburned hydrocarbons, carbon monoxide, nitrogen oxides, which may be referred to as NOx molecules, and aerosols. Operation may be monitored by one or more sensing devices located in the exhaust gas inlet, including, for example B. a NOx sensor. Operation may also be determined using simulation models that are dynamically executed during operation.

Selective catalytic reduction catalysts (SCRs) may use reducing agents to reduce NOx molecules to elemental nitrogen. A known reducing agent is urea, which can be converted into ammonia (NH3) in an exhaust system. The reductant may be injected into the exhaust feedstream upstream from one or more selective catalytic reduction catalysts and may be stored on a surface or otherwise captured for use in the reduction of NOx molecules to elemental nitrogen and water.

The signal output from a downstream NOx sensor may have cross-sensitivity between NOx molecules and NH3 molecules when it is arranged to monitor an exhaust gas feed downstream of an SCR. As such, known reductant injection control systems operating in a reductant injection control scheme may operate in an underdosage or an overdose condition, depending on the size of the NH3 exiting the SCR. An open loop reductant control system may result in reduced performance of an SCR that is sensitive to hardware variation and, under certain operating conditions, may result in false-positive output from a diagnostic monitoring routine for an SCR.

SUMMARY

There is described an internal combustion engine in fluid communication with an exhaust aftertreatment system. The exhaust aftertreatment system includes a selective catalytic reduction device (SCR), a NOx sensor arranged to monitor the exhaust gas feedstream downstream of the SCR, and an injection system arranged to inject a reductant into the exhaust gas feed upstream relative to the SCR. One method of controlling the reductant injection system to inject reductant into the upstream exhaust relative to the SCR includes monitoring engine operation and determining an initial reductant dosing rate responsive to engine operation. A dosing disorder is induced in the reducing agent dosage rate. The exhaust gas feed is monitored via the NOx sensor and a reductant dosing correction term is determined based on the monitoring. A final dosage rate for controlling the reductant injection system is determined based on the initial reductant dosing rate, the dosing error, and the reductant dosing correction term.

The foregoing features and advantages as well as other features and advantages of the present teachings will become more apparent from the following detailed description of some of the best modes and other modes for carrying out the present teachings with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments will now be described by way of example with reference to the accompanying drawings, in which:

1 schematically illustrates an internal combustion engine in fluid communication with an exhaust aftertreatment system, including an oxidation catalyst disposed upstream of a selective catalytic reduction device (SCR) and a particulate filter according to the disclosure;

2 FIG. 12 schematically illustrates a closed loop reductant injection control routine that may be employed to control upstream of an SCR that is an element of an exhaust aftertreatment system, with reference to FIG 1 to purify exhaust gases generated as a by-product of combustion in an internal combustion engine according to the disclosure; and

3 FIG. 16 graphically illustrates a signal output output from an exemplary NOx sensor, eg, the NOx sensor signal output from an embodiment of the second exhaust gas sensor, wherein the signal output in accordance with the disclosure indicates cross-sensitivity between NOx and NH3.

DETAILED DESCRIPTION

Reference is now made to the drawings, in which the drawings are only illustrative of certain exemplary embodiments, but are not intended to be limiting thereof 1 schematically an exemplary internal combustion engine (engine) 100 illustrated with an exhaust aftertreatment system 50 fluidly coupled, which is arranged according to an embodiment of this disclosure. The motor 100 is a multi-cylinder internal combustion engine that burns a mixture of directly injected fuel with intake air and recirculates exhaust to produce mechanical power. The motor 100 is implemented as a compression ignition engine, as shown, but the concepts described herein may be applied to other engine configurations that include embodiments of the exhaust aftertreatment system described herein 50 use. The motor 100 Can be used in ground vehicles, such as cars, trucks, agricultural vehicles or construction vehicles, marine vehicles, but also in marine vehicles or in stationary applications, such. B. connected to a power generator. As used herein, the term "upstream" and similar terms refers to elements that are indicative of flow flow relative to a specified location, and the term "downstream" and related terms refer to elements that are relative to generation of flow flow are removed to a specified position.

The motor 100 preferably includes an engine block 7 with several cylinders, an intake manifold 8th for channeling the intake air into the cylinders of the engine 100 and an exhaust manifold 9 for transporting the exhaust gas for channeling through the exhaust aftertreatment system 50 , Other engine components and systems, not shown, include pistons, crankshaft, cylinder heads, intake valves, exhaust valves, camshafts and, if used, variable camshaft phasers. The motor 100 preferably operates in a four-stroke combustion cycle of repetitively executed cycles of intake-compression-combustion-exhaust. A variable geometry turbocharger (VGT) includes a turbine in one embodiment 28 in fluid communication with the exhaust manifold 9 upstream relative to the exhaust aftertreatment system 50 , The motor 100 includes a variety of direct fuel injectors 47 , which are arranged so that the fuel is injected directly into the individual combustion chambers. The injectors 47 may be any suitable direct injection devices, such as solenoid operated devices in one embodiment. Fuel is delivered via a low-pressure fuel pump 41 , a fuel filter assembly 42 , a high-pressure fuel pump 43 , a fuel metering valve 44 , a fuel rail 45 and a pressure control valve 46 from a fuel tank to the injectors 47 delivered. Each of the engine cylinders preferably includes a glow plug 25 , The motor 100 includes an air intake system that has an intake air filter 48 , an air mass sensor 49 , a compressor 10 of the VGT, a charge air cooler 11 , a throttle valve 13 , a sensor 12 for monitoring boost pressure and intake air temperature as well as other measuring devices that may be useful. The motor 100 includes an exhaust gas recirculation (EGR) that keeps the exhaust gases flowing from the exhaust manifold 9 to the intake manifold 8th transported. In one embodiment, the EGR system may be an EGR valve 14 , an EGR cooler 17 with a bypass valve 15 , an EGR outlet temperature sensor 18 , an EGR cooler inlet temperature sensor 31 and a vacuum switch 16 include. The intake manifold 8th can also have several swirl valves 19 for mixing the intake air with the recirculated exhaust gases. Other engine monitoring sensors may include a crankshaft position sensor 20 , a camshaft position sensor 21 , a coolant temperature sensor 22 , an oil level switch 23 and an oil pressure switch 24 include, among others. One or more engine monitoring sensors may be replaced by a suitable executable model.

A motor control 26 monitors various sensors and performs control routines to instruct various actuators to control the operation of the engine 100 in response to the user commands. User commands can come from different user input devices, eg. B. a pedal assembly 27 which includes, for example, an accelerator pedal and a brake pedal. Other sensors related to the operation of the engine may be exemplified, among others, an air pressure sensor (not shown), an ambient air temperature sensor (not shown), a VGT position sensor (not shown), the exhaust gas temperature sensor 31 , a charge air inlet temperature sensor 32 and a charge air outlet temperature sensor 33 be.

The exhaust aftertreatment system 50 may include a variety of fluidly connected exhaust gas purifying devices for purifying exhaust gases prior to discharge into the ambient air. An exhaust gas purifying device may be any one Be device that is configured to components of the exhaust gas inlet 51 to oxidise, reduce, filter and / or otherwise treat, including, but not limited to, hydrocarbons, carbon monoxide, nitrogen oxides (NOx) and particulate matter. In the illustrated embodiment, the first, second and third exhaust gas purifying devices 53 . 54 and 55 respectively implemented. The first and second exhaust gas purification devices 53 . 54 Can work closely with the exhaust manifold 9 be connected, ie be arranged in an engine compartment. The third exhaust gas purifying device (catalyst) 55 may be remotely located, such as in the underbody paneling when used in a ground vehicle. The first exhaust gas cleaning device 53 For example, in certain embodiments, it may be an oxidation catalyst for the oxidation of hydrocarbons and other constituents in the exhaust gas feed, and is hereinafter referred to as an oxidation catalyst 53 designated. The second exhaust gas cleaning device 54 may be a selective catalytic reduction catalyst hereinafter referred to as SCR 54 referred to as. In one embodiment, the SCR 54 also include a particulate filter for filtering particulate matter from the exhaust gas feed. A reductant delivery system 60 including a reductant injector 62 with injector may be arranged upstream to controllably introduce reductant into the exhaust gas feed to facilitate the reduction of NOx. The third catalyst 55 may be a second oxidation catalyst for oxidizing NH3 generated by the SCR 54 can pass through. Some embodiments may use the third catalyst 55 do not use. In an embodiment, the first SCR 54 may be a urea-based device and the injected reducing agent may be urea. As can be seen by those skilled in the art, urea can be converted to ammonia (NH3) on the substrate of the SCR 54 can be stored and reacted with NOx molecules for reduction to form elemental nitrogen (N2) and other inert gases.

Both the oxidation catalyst 53 , the SCR 54 as well as the third catalyst 55 include a ceramic or metallic substrate having flow channels coated with suitable materials, including but not limited to, for example, platinum group metals such as platinum, palladium, and / or rhodium; other metals such as copper; Cer and other materials. The coated materials effect chemical reactions to oxidize, reduce, filter, or otherwise treat constituents of the exhaust gas feed under certain conditions of temperature, flow rate, air / fuel ratio, and others. The illustrated embodiment includes the elements of the exhaust aftertreatment system 50 in an arrangement. In an alternative embodiment, the particulate filter and oxidation catalyst may act collectively on a single substrate as part of the oxidation catalyst 53 be arranged and assembled in a single mechanical assembly. In the context of this disclosure, other embodiments of the components of the exhaust aftertreatment system 50 In addition, such arrangements may additionally include other exhaust gas cleaning devices or must contain no other exhaust gas cleaning devices, depending on the requirements of the corresponding application.

Sensors for monitoring the exhaust gas aftertreatment system's exhaust gas purification devices 50 can each have a first and a second exhaust gas sensor 58 . 61 one or more particulate matter sensors 56 and a delta pressure sensor 57 to monitor the pressure drop in the SCR 54 , one or more temperature sensors 59 and / or other suitable sensors and models for exhaust gas feed monitoring. The first and the second exhaust gas sensor 58 . 61 are preferably configured as NOx sensors and, in one embodiment, may include a wide-range lambda detection capability. Such sensors and models may be arranged to monitor or otherwise determine parameters relating to the exhaust gas feed at particular locations. As such, the aforementioned sensors and / or models can be advantageously used to monitor the performance of individual exhaust gas purifying devices, to monitor parameters related to the performance of the individual exhaust gas purifying devices, to monitor the performance of a subset of the exhaust gas purifying devices, or to monitor performance the entire exhaust aftertreatment system 50 to monitor. The first exhaust gas sensor 58 Preferably, it is arranged so as to position the exhaust gas upstream relative to the oxidation catalyst, as shown 53 supervised. Alternatively or additionally, the first exhaust gas sensor 58 be arranged to the exhaust gas inlet downstream of the oxidation catalyst 53 (not shown) to monitor. The second exhaust gas sensor 61 is arranged to the exhaust gas inlet downstream with respect to the SCR 54 to monitor. The first and the second exhaust gas sensor 58 . 61 may be fabricated as a planar zirconia dual field device with a sensor element and an integrated, electrically operated heating element.

The engine controller preferably includes the control of various engine operating parameters, including control of preferred engine control conditions to minimize various exhaust gas constituents through, for example, and without, chemical reaction processes restrict oxidation, reduction, filtering and selective reduction. Other engine control states involve the control of engine warm-up operating parameters 100 and for heat transfer or otherwise heating the first oxidation catalyst 53 , the SCR 54 and the third catalyst 55 in order to achieve effective operation thereof.

The terms control unit, control module, module, controller, controller, processor and the like refer to one or more combinations of application specific integrated circuits (ASIC), electronic circuit (s), central processing unit (s), e.g. B. Microprocessor (s) and their associated non-transitory memory components in the form of memory and data storage devices (read-only memory, programmable read-only memory, random access memory, hard disk memory, etc.). The non-transitory memory component is capable of executing machine readable instructions in the form of one or more software or firmware programs or routines, combinatorial logic circuitry, input / output circuitry and devices, signal conditioning and buffer circuits, and store other components that may be accessed by one or more processors to provide described functionality. Input and output devices and circuits include analog-to-digital converters and similar devices that monitor sensor inputs at a predetermined fetch frequency or in response to a triggering event. Software, firmware, programs, commands, control routines, code, algorithms, and similar terms refer to all instruction sets executable by a controller, such as a computer. B. Calibrations and Tables. Each controller executes control routines to provide the desired functions, including monitoring the inputs of sensor devices and other networked controllers, as well as executing control and diagnostic routines to control actuation of actuators. The routines can be used at regular intervals, such as. B. during running operation every 100 microseconds to run. Alternatively, routines may be executed in response to a triggering event. The communication between the controllers, as well as between the communications between the controllers, actuators, and / or sensors, may be accomplished over a point-to-point direct cabling, network communication bus connection, wireless connection, or other suitable communication link. Communication involves exchanging data signals in any suitable manner, including, but not limited to, communications. As electrical signals via a conductive medium, electromagnetic signals through the air, optical signals via optical fibers and the like. Data signals may include discrete, analog or digitized analog signals representing inputs from sensors and actuator commands, as well as communication signals between controllers. The term "signal" refers to any physically perceptible display that transmits information and may include any suitable waveform (eg, electrical, optical, magnetic, mechanical, or electromagnetic), such as DC, AC, sine, triangular, square, Vibration and the like that can pass through a medium. The term "model" refers to a processor-based or processor-executable code and associated calibration that simulates the physical existence of a device or physical process. As used herein, the term "dynamic" describes steps or methods that may be performed in real time and may include monitoring or otherwise determining parameter states, and periodically or periodically updating parameter states when executing a routine or between iterations in executing the routine.

2 schematically illustrates a closed loop reductant injection control routine 200 which may be employed to control upstream of an SCR, which is an element of an exhaust aftertreatment system, for exhaust gases generated as a by-product of combustion in an internal combustion engine. Such an embodiment of an aftertreatment system is described with reference to FIG 1 including the SCR 54 , the reducing agent injection nozzle 62 , the temperature sensor 59 and the NOx sensor 61 , The reductant injection control routine with closed loop 200 includes an initial dosing routine 201 , a fault routine 220 and a feedback routine 260 which cooperate to give a final reductant dosage rate 225 which can be used to control the reductant injection and ammonia storage on the SCR 54 to manage something.

Overall, the closed loop reductant injection control routine includes 200 engine operation and other factors to an initial reductant dosing rate 214 which is responsive to engine operation and a time varying dosing error 222 at the initial reductant dosing rate 214 induced. During operation, the exhaust gas feed becomes downstream of the SCR 54 via the second exhaust gas sensor 61 supervised. A reductant overdose and associated ammonia slip or reductant underdose and associated NOx breakthrough may be based on the induced time variable dosage disorder 222 in the Reduktionsmitteldosierungsrate, the engine operation and the input of the exhaust gas sensor 61 , the exhaust feed downstream with respect to the SCR 54 monitored, determined. A reductant overdose and an associated ammonia slip may be indicated when the input from the second exhaust gas sensor 61 not with an estimated amount of NOx breakthrough coming from the SCR 54 is spent correlates. A reductant underdose and an associated NOx breakthrough may be indicated when the input from the second exhaust gas sensor 61 with the estimated amount of NOx breakthrough detected by the SCR 54 is spent correlates.

A reductant dosing correction term 255 can be generated based on it. A final reductant dosing rate 225 for controlling the reducing agent injection nozzle 62 of the reducing agent injection system 60 is based on the initial reductant dosing rate 214 , the time-variable dosing disorder 222 and the presence of the reducing agent in the exhaust gas inlet determined. The final reductant dosing rate 225 can be used to control the reductant injection to provide ammonia storage on the SCR 54 to manage something.

The initial dosing routine 201 determines the initial reductant dosing rate 214 as follows. Inputs to the initial routine 201 preferably include a plurality of sensed or estimated engine and exhaust system operating parameters, preferably the SCR temperature 202 , the exhaust gas mass flow rate 204 and other parameters 207 concern, referring to the exhaust gas inlet 51 such as air / fuel ratio and exhaust components such as NO, NO 2, O 2, etc. The operating parameters may be directly monitored or derived based on monitored operating conditions of the engine. Other parameters may include exhaust temperature and space velocity for the SCR 54 wherein the space velocity is based on a displaced volume (ml) of the SCR 54 and a volumetric flow rate (l / s) of the exhaust gas. Those skilled in the art are capable of determining the space velocity for the exhaust aftertreatment devices, such as the SCR 54 to be determined by reference to 1 is described.

The initial dosing routine 201 includes a model section 210 to determine an effective amount of ammonia, based on the detected or estimated engine and exhaust system operating parameters and a final reductant dosing rate 225 on the SCR 54 wherein the final reductant dosage rate 225 preferably the time-varying dosage disorder 222 includes. The model section 210 includes a one-dimensional kinetic model of the SCR 54 , One-dimensional kinetic models of SCRs are known to those skilled in the art. The model section 210 produces outputs that contain an estimated amount of stored ammonia 211 , an estimated ammonia consumption rate 213 and an estimated ammonia and NOx breakthrough 209 included by the SCR 54 based on the detected or estimated engine and exhaust system operating parameters.

The SCR temperature 202 and the exhaust mass flow rate 204 be on an SCR ammonia storage model 205 applied to an ammonia storage setpoint 206 to determine who the SCR 54 assigned. The SCR ammonia storage model 205 shows a maximum ammonia storage capacity for the SCR 54 on the basis of its temperature and its space velocity, to the ammonia storage setpoint 206 becomes. Injecting additional amounts of ammonia into the exhaust gas feedstream may result in the breakthrough of ammonia, referred to as ammonia slip. States of temperatures, space velocities and other operating parameters are application specific and may be determined by known engineering practices during product development or otherwise determined. The ammonia storage setpoint 206 and the estimated amount of stored ammonia 211 are subtracted arithmetically and by a gain factor 212 adjusted, and the result is estimated by the ammonia consumption rate 213 arithmetically reduced to the initial reductant dosing rate 214 to determine.

The fault routine 220 generates the time-varying dosing error 222 , The time-varying dosing disorder 222 may be a signal that is sinusoidal and has a magnitude that is +/- 10% of a maximum size of the reductant dosing and a period of 10+ seconds in one embodiment. Other perturbation schemes of different shapes, magnitudes, and periods may be employed, and thus fall within the scope of this disclosure.

The feedback routine 260 includes a correlation routine 240 and a control routine 250 with open loop. Entries in the feedback routine 260 include the SCR temperature 202 , the estimated ammonia and NOx breakthrough 209 and the estimated amount of stored ammonia 211 that from the initial dosing routine 201 be provided, and a sensor signal 235 that of the second exhaust gas sensor 61 is issued.

3 graphically shows a signal generated by an exemplary NOx sensor, e.g. For example, the NOx sensor signal generated by an embodiment of the second exhaust gas sensor 61 is produced. The NOx sensor generates an output signal that responds to nitrogen, detecting both NOx molecules and ammonia (NH3) molecules. As such, the signal output from the NOx sensor has a cross sensitivity between NOx and NH3. The graph includes a combined size of NOx and NH3 302 on the vertical axis with respect to the stored NH3 304 on the horizontal axis. The recorded parameters include the NOx sensor signal 312 , NOx 314 and NH3 316 , A preferred operating point 305 , which includes an engine operation that achieves a low NOx state in combination with a low NH3 state. If the NH3 316 increases, the NOx sensor signal decreases 312 to, as by the lines to the right of the preferred operating point 305 is specified. If the NOx 314 increases, the NOx sensor signal decreases 312 to, as by the lines to the left of the preferred operating point 305 is specified.

Referring again to 2 allows the addition of the time-varying dosing error 222 to the initial reductant dosage rate 214 the distinction between the increasing NH3 slip and the increasing NOx breakthrough based on the NOx sensor signal 235 , As such, there has been a decrease in the initial reductant dosing rate 214 a corresponding effect on the signal from the NOx sensor signal 235 which is related to an increase in NOx emissions, ie NOx breakthrough. In contrast, there has been an increase in the initial reductant dosing rate 214 a corresponding effect on the signal from the NOx sensor signal 235 and that refers to an increase in NH3 slip.

The correlation routine 240 determines a statistical correlation between the sensor signal 235 and each of the estimated amount of stored ammonia 211 , the estimated NOx breakthrough 209 and the SCR temperature 202 , preferably in a period of time which is the same as the dosage disturbance period. The statistical correlation between the sensor signal 235 and each of the estimated amount of stored ammonia 211 , the estimated NOx breakthrough 209 and the SCR temperature 202 is preferably in the form of a time-synchronized correlation of the aforementioned terms taking into account the relationship between the NOx sensor signal NH3 and the NOx, with reference to 3 is described. The correlation routine 240 generates a correction term 245 which is based on one of the aforementioned correlations or a combination thereof. The correction term 245 is determined from the correlation and the SCR out NOx sensor signal. As an example, the correction term may be determined from the multiplication between the correlation and the sinusoidal wave amplitude released from the SCR out NOx sensor signal at the same frequency as the dosing disturbance frequency.

The correction term 245 goes to the control routine 250 which includes a suitable proportional-integral (PI) control routine or a suitable proportional-integral-derivative (PID) control routine which determines the reductant dosing correction term thereon 255 generated. The goal is to use the correction term 245 to control at a desired level. PI and PID control routines are known to those skilled in the art and will not be described further herein. The initial reductant dosing rate 214 , the time-varying dosing disorder 222 and the reductant dosing correction term 255 are additively combined to give the final reductant dosage rate 225 for controlling the reductant delivery system 60 including the reducing agent injection nozzle 62 to determine.

The concepts described herein include a method of distinguishing NO x or NH 3 from a NOx sensor signal by continuously disturbing an NH 3 metering rate with a given sine wave frequency and correlating the SCR out NOx sensor signal with an estimated SCR out NOx. , NH3 storage or temperature in a time period consistent with the dosing disturbance period. A correction term can be determined from the correlations, and an extracted signal can be determined from the SCR-out NOx sensor signal. A closed loop routine is then used to control the correction term at a desired level using PID control to generate the reductant dosing correction term. The method should be used for the closed-loop dosing control to precisely control the SCR-NH3 storage to reduce the SCR NOx reduction efficiency variation caused by the SCR hardware and operating state variability and the NH3 Consumption minimized. The method can also be used to reduce SCR efficiency and monitor erroneous tripping.

As described herein, the signal output by the NOx sensor arranged after the SCR may be identified as being associated with increased NOx emissions or increased NH3 emissions when subjected to the continuous disturbance of the NH3 metering rate associated with the estimated SCR-out NOx emissions is correlated. The referring to 2 described reduction injection control routine 200 closed loop may be advantageously used to reduce the NOx reduction variation, while the NH3 consumption and breakthrough in one embodiment of the aftertreatment system 50 , referring to 1 is minimized using such a correlation.

The flowchart and block diagrams in the flowcharts illustrate the architecture, functionality, and operation of possible implementations of systems, methods, and computer program products according to various embodiments of the present disclosure. In this regard, each block in the flowcharts or block diagrams may represent a module, segment or portion of code that includes one or more executable instructions for implementing the specified logical function (s). It is also to be understood that each block of block diagrams and / or flowchart illustrations and combinations of blocks in the block diagrams and / or flowchart illustrations are provided by specialized hardware based systems that perform the specified functions or operations or combinations of special purpose hardware and computer instructions can be implemented. These computer program instructions may also be stored in a computer readable medium that may control a computer or other programmable data processing device to function in a particular manner such that the instructions stored in the computer readable medium produce an article of manufacture, including instruction means, having the function / Process indicated in the flowchart and / or block diagram block or blocks.

However, while the detailed description and drawings or figures are supportive and descriptive of the present teachings, the scope of the present teachings is defined solely by the claims. While a few of the best modes and other modes for carrying out the present teachings have been described in detail, there are several alternative constructions and embodiments for implementing the present teachings defined in the appended claims.

Claims (10)

 A method of controlling reductant injection into an exhaust aftertreatment system for an internal combustion engine, wherein the exhaust aftertreatment system includes a selective catalytic reduction device (SCR), a NOx sensor arranged to monitor the exhaust gas feedstream downstream of the SCR, and a reductant injection system is arranged to inject reducing agent into the exhaust gas feed upstream relative to the SCR, the method comprising: monitoring engine operation; determining an initial reductant dosing rate in response to engine operation; inducing a dosage disorder in the initial reductant dosage rate; monitoring the exhaust gas feed via the NOx sensor; determining, via a controller, a reductant dosing correction term based on the monitored exhaust gas feed via the NOx sensor; determining a final dosage rate for controlling the reductant injection system based on the initial reductant dosing rate, the dosing disorder, and the reductant dosage correction term; and controlling the reductant injection system based on the final dosage rate.  The method of claim 1, wherein the dosing error in the reductant dosing rate comprises a time varying dosing error in the reductant dosing rate.  The method of claim 2, wherein the time varying dosage disorder in the reducing agent dosage rate comprises a sinusoidal time varying dosage disorder.  The method of claim 1, wherein determining, via a controller, a reductant dosing correction term based on the monitored exhaust gas feed via the NOx sensor comprises: estimating the NOx breakthrough performance of the SCR based on the operating parameters of the engine and exhaust systems; correlating the estimated NOx breakthrough from the SCR and the monitored exhaust gas feed via the NOx sensor; and determining the redundant dosing correction term based on the correlation of the estimated NOx breakthrough output by the SCR and the monitored exhaust gas feed via the NOx sensor. The method of claim 4, wherein the redundant dose correction term is a Indicates reductant overdose when the estimated NOx breakthrough output by the SCR does not correlate with the monitored exhaust gas feed via the NOx sensor.  The method of claim 5, wherein the estimated NOx breakthrough output by the SCR does not correlate with the monitored exhaust gas feed via the NOx sensor when a signal output from the NOx sensor does not correlate with the estimated amount of NOx breakthrough output from the SCR.  The method of claim 4, wherein the redundant dosing correction term indicates reductant dosing when the estimated NOx breakthrough output from the SCR correlates to the monitored exhaust gas feed via the NOx sensor.  The method of claim 7, wherein the estimated NOx breakthrough output by the SCR correlates to the monitored exhaust gas feed via the NOx sensor when a signal output from the NOx sensor correlates to the estimated amount of NOx breakthrough output from the SCR.  The method of claim 4, further comprising using a proportional integral derivative (PID) controller to control the reductant injection system based on the final dosage rate.  An exhaust after-treatment system and a controller arranged to purify an exhaust gas inlet for an internal combustion engine, comprising: a selective catalytic reduction device (SCR) disposed downstream relative to an oxidation catalyst; a NOx sensor arranged to monitor the exhaust gas inlet downstream relative to the SCR; a reductant injection system for injecting reductant into the exhaust feed upstream relative to the SCR; and and wherein the controller is operatively connected to the reductant injection system and wherein the controller is in communication with the NOx sensor and includes an instruction set, the instruction set being executable for: Monitoring the operation of the internal combustion engine, Determining an initial reductant dosing rate in response to engine operation, Inducing a dosage disturbance in the reducing agent dosage rate, Monitoring the exhaust gas inlet via the NOx sensor, Determining a reductant dosing correction term based on the monitored exhaust gas feed via the NOx sensor, Determining a final dosage rate for controlling the reductant injection system based on the initial reductant dosing rate, the dosing disorder, and the reductant dosing correction term, and Controlling the reductant injection system based on the final dosage rate.

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